One of the nice things about electric cars, reviewers often mention, is they are blissfully quiet; freed from the need for an internal combustion engine exploding chambers of gasoline thousands of times every minute, they tend to make minimal amounts of noise.

They’re so quiet, in fact, that it can be a problem — a problem big enough that federal regulators have stepped in with a plan (PDF) to make the cars play a sound of their own. Pedestrians — visually impaired ones especially, but also those blessed with fine eyesight — often hear an oncoming vehicle without seeing it. By being so eerily quiet, electric cars pose a safety risk, so the logic goes.

The basics are that electric cars should produce a sound when in reverse, and when driving at speeds of up to 30 km/h. One proposal was for the sound to be a recording of what an regular gas-powered car sounds like, but that idea was quickly dismissed because it “would not ensure sufficient detectability.”